The endoplasmic reticulum (ER) is an organelle of the endomembrane system within a cell. It consists of a network of tubules and sacs called cisternae. The ER’s internal compartment (lumen) is separated from its cytosol exterior by a membrane that is a continuation of the cell’s nuclear envelope. It was first discovered by Keith R. Porter, Albert Claude, and Ernest F. Fullam in 1945.
Primary Functions:
o Protein translation and synthesis
o Sequestration of calcium
o Production of lipids and steroids
o Storage and production of glycogen
o Insertion of membrane proteins
Rough Endoplasmic Reticulum (RER):
o Surface is covered with ribosomes and gives the RER a “rough” appearance through an electron microscope
o Ribosomes on the RER’s surface grow polypeptide chains, which are then sent to the lumen through a pore in the ER’s membrane. The proteins then fold inside the lumen into their natural shape. Most of the ER’s secretory proteins are glycoproteins or proteins with carbohydrates bonded to them. These proteins are moved in transport vesicles to the smooth endoplasmic reticulum, the golgi apparatus, or the cell membrane.
Smooth Endoplasmic Reticulum (SER):
o Produces lipids and steroids, metabolizes carbohydrates
o Holds the enzyme glucose-6-phosphatase which converts glucose-6-phosphate through gluconeogenesis into glucose
o Liver Cells: detoxifies with enzymes that usually incorporate hydroxyl group to make the drug more soluble and easier for the body to rid
o Muscle Cells: after nerve impulses are stimulated, stored calcium ions in the cytosol travel through the ER membrane into the lumen and create a muscle cell contraction
Research on the Endoplasmic Reticulum
Diseases caused due to ER stress
o The Burnham Institute for Medical Research, La Jolla, California, USA
o Researchers: Chunyan Xu, Beatrice Bailly-Maitre and John C. Reed
o ER stress can cause hypoxia, neurodegenerization, heart disease, and diabetes
o BI-1 (Bax-inhibitor) is an ER protein that suppresses cell death pathways (apoptosis)
o The Bax-Inhibitor is secreted when ER undergoes stress in effort to compensate for damage and causes the unfolded protein response (UPR)
o Although the ER stress is enigmatic, here are some possible factors that could affect the ER:
• Deprivation of glucose
• Viral infection
Insertion of Secretory Proteins into the membrane
o New York University
o Researcher: David Domingo Sabatini Ph.D., Doc. En Med.
o Research Summary: The effecting elements on the insertion of the proteins secreted in the Endoplasmic Reticulum into the membrane.
o Currently: Their research uses an artificial environment that allows them to trace specific proteins, their sorting, and the protein’s transfer to the membrane.
MLA Works Cited
"Endoplasmic Reticulum." Wikipedia, The Free Encyclopedia. 9 Oct. 2008
<http://en.wikipedia.org/wiki/Endoplasmic_reticulum>.
Beatrice Bailey-Maitre, Ph.D. “Role of BI-1 Protein in Brest Cancer Apoptosis.” The Burnham Institute for Medical Research. 10 Oct. 2008.
<http://www.cbcrp.org/RESEARCH/PageGrant.asp?grant_id=3756>
Beatrice Bailey-Maitre, Ph.D. “BI-1 regulates an apoptosis pathway linked to endoplasmic reticulum stress.” The Burnham Institute for Medical Research. 10 Oct. 2008.
<http://lib.bioinfo.pl/pmid:15304216>
Xu Chunyan, Beatrice Bailey-Maitre, and Reed John C. “Endoplasmic reticulum stress: cell life and death decisions.” The Journal of Clinical Investigations. 10 Oct. 2008.
< http://www.jci.org/articles/view/26373>
Sabatini, David Domingo, Ph.D., Doc. en Med. "David Domingo Sabatini Ph.D., Doc.
en Med." NYU Langone Medical Center. 2008. 9 Oct. 2008
<http://www.med.nyu.edu/research/sabatd01.html>.
Campbell, Neil A. Biology. 8th ed. San Francisco: Pearson Education, Inc., 2008.
“Endoplasmic_Reticulum.jpg” 10 October 2008.
<http://www.microscopy.fsu.edu/cells/endoplasmicreticulum/images/endoplasmicreticulumfigure1.jpg>
“ribos2.jpg” 10 Oct. 2008.
<http://www.cytochemistry.net/Cell-biology/ribos2.jpg>
“home_page_image.jpg” 10 Oct. 2008.
< http://pathology.ucsf.edu/oakes/images/home_page_image.jpg>
Maggie Fuller
Plant Cell (Rinehart)
Animal Cell (Rinehart)
Rough ER
(Mallery)
The "rough" portion of the endoplasmic reticulum (RER) is so named because of the attached ribosomes on the cytoplasmic side of the RER sacs which give the organelle a granular appearance. This section of the ER is located closer to the nucleus than the smooth ER and is "continuous with the nuclear envelope" (Campbell 58). The ER itself is continuous, meaning that the membrane is a single unit, connecting seamlessly with the nuclear envelope. In plant cells, this membrane also forms intracellular connections via the plasmodesmata (Davidson). The rough membranes of the endoplasmic reticulum were first seen by Keith R. Porter, Albert Claude, and Ernest F. Fullam in 1945 when they created the first ever electron micrograph of an intact cell ("History").
Modification of Proteins
The ribosomes on the surface of RER create the ingredients for proteins. When these ingredients enter the RER sacs, they are modified into functioning proteins by adjusting the tertiary and quaternary structures of the proteins (Campbell 59). The type of proteins synthesized depends on the type of cell that encompasses the RER. For example, in white blood cells, RER produces antibodies, and in pancreatic cells, it produces insulin (Mallery). "Chaperone proteins" check that all proteins are folded properly before they are transported from the RER (Papp). We know very little about these proteins and research is being conducted to study the effects of high and low levels of chaperone.
Making More Membrane
The proteins synthesized in the RER either move into the Smooth Endoplasmic Reticulum or are used as part of the RER membrane. If the proteins are membrane proteins, they are inserted into the membrane, which over time grows and enlarges the organelle. The more active in protein synthesis the RER is, the more membrane it produces (Spurger). This makes the identification of highly protein-synthesizing cells very easy because the large RER region marks its activity.
Smooth ER (SER)
SER in Liver Cell (Spurger)
The membrane and proteins made in the RER move into the SER to be "transferred to other parts of the cell," usually to the Golgi Apparatus or the cell membrane for export ("Journey into the Cell:"). The SER is connected to the RER farther away from the nucleus. It is tubular in shape and does not have ribosomes attached to it. The specific functions of the SER are highly dependent upon the type of cell in which it exists. Here are a few of its many functions.
SER in Liver Cells
In liver cells, SER metabolizes glycogen and detoxifies many drugs (Spurger). You can see in the picture above how large the SER is in the liver cell. This is because the more the SER processes, the larger it becomes. This can be potentially harmful because it raises tolerance to drugs, increasing the likelihood of larger doses consumed by drug abusers and increasing tolerance to other essential drugs like antibiotics (Campbell 58).
SER in Muscle Tissue
In many muscle cells SER serves as a store of Calcium. When nerve impulses reach the muscle cell, the SER releases its Calcium (Campbell 59). This action works with Calcium pumps to contract the cell and allow the muscle to move (Spurger).
Production of Steroids
In the adrenal cortex, the SER is responsible for synthesis of many essential steroid hormones. The SER passes unfinished molecules back and forth with the mitochondria to make minor changes in the molecule until it is completely finished (King). In gonadal tissue, the ER contains an enzyme aromatase, which converts testosterone and androstenedione to estradiol (King). This function is incredibly important because the sensitivity of humans to sex hormone level fluctuations.
Aromatase Sex Hormone Conversion (King)
Works Cited
1)Black, Virginia H., et al. “Cholesterol and Steroid Synthesizing Smooth Endoplasmic Reticulum of Adrenocortical Cells Contains High Levels of Proteins Associated with the Translocation Channel.” Endocrinology 146.10 (2005): 4234-4249. Abstract. Endocrinology. 2005. The Endocrine Society. 13 Oct. 2008 <http://endo.endojournals.org/cgi/content/abstract/146/10/4234>.
2)Campbell, Neil A., et al. Biology: concepts and connections. 5th ed. 7 vols. San Francisco: Pearson, 2006. 50-69.
3)Davidson, Michael W. “The Endoplasmic Reticulum.” Molecular Expressions Cell Biology. 13 Dec. 2004. The Florida State University Research Foundation. 12 Oct. 2008 <http://www.microscopy.fsu.edu/cells/endoplasmicreticulum/endoplasmicreticulum.html>.
4)“History.” Ernest F. Fullam Inc. Ernest F. Fullam Inc. 13 Oct. 2008 <http://www.fullam.com/History.htm>.
5)“Journey into the Cell: The Endoplasmic Reticulum.” Biology. 2008. The New York Times Company. 12 Oct. 2008 <http://biology.about.com/library/weekly/aa041300a.htm>.
6)King, Michael W. “Steroid Hormones.” The Medical Biochemistry. 15 May 2008. Indiana University School of Medicine. 13 Oct. 2008 <http://themedicalbiochemistrypage.org/steroid-hormones.html>.
7)Mallery, Charles H. “Major Eukaryotic Cell Organelles.” University of Miami Department of Biology. 9 Oct. 2008. University of Miami. 11 Oct. 2008 <http://porpax.bio.miami.edu/~cmallery/150/cells/organelle.htm>.
8)Papp, Eszter, et al. “Changes of Endoplasmic Reticulum Chaperone Complexes, Redox State, and Impaired Protein Disulfide Reductase Activity in Misfolding {Alpha}1-Antitrypsin Transgenic Mice.” The FASEB Journal (Oct. 2006). 13 Oct. 2008 <http://www.fasebj.org/cgi/content/abstract/20/7/1018>.
9)Rinehart, Claire. “Eukaryotic Organelles.” Introduction to Molecular and Cell Biology, Biol. 220. 2004. Western Kentucky University. 12 Oct. 2008 <http://bioweb.wku.edu/courses/Biol22000/11Organelles/Lecture.html>.
10)Spurger, Linda. “Cell Biology.” Cell Biology Graduate Program. 5 Dec. 2003. The University of Texas Medical Branch. 13 Oct. 2008 <http://cellbio.utmb.edu/cellbio/>.
Endoplasmic Reticulum (ER)
Larson Stimson, Per. G
The endoplasmic reticulum (ER) is an organelle of the endomembrane system within a cell. It consists of a network of tubules and sacs called cisternae. The ER’s internal compartment (lumen) is separated from its cytosol exterior by a membrane that is a continuation of the cell’s nuclear envelope. It was first discovered by Keith R. Porter, Albert Claude, and Ernest F. Fullam in 1945.
Primary Functions:
o Protein translation and synthesis
o Sequestration of calcium
o Production of lipids and steroids
o Storage and production of glycogen
o Insertion of membrane proteins
Rough Endoplasmic Reticulum (RER):
o Surface is covered with ribosomes and gives the RER a “rough” appearance through an electron microscope
o Ribosomes on the RER’s surface grow polypeptide chains, which are then sent to the lumen through a pore in the ER’s membrane. The proteins then fold inside the lumen into their natural shape. Most of the ER’s secretory proteins are glycoproteins or proteins with carbohydrates bonded to them. These proteins are moved in transport vesicles to the smooth endoplasmic reticulum, the golgi apparatus, or the cell membrane.
Smooth Endoplasmic Reticulum (SER):
o Produces lipids and steroids, metabolizes carbohydrates
o Holds the enzyme glucose-6-phosphatase which converts glucose-6-phosphate through gluconeogenesis into glucose
o Liver Cells: detoxifies with enzymes that usually incorporate hydroxyl group to make the drug more soluble and easier for the body to rid
o Muscle Cells: after nerve impulses are stimulated, stored calcium ions in the cytosol travel through the ER membrane into the lumen and create a muscle cell contraction
Research on the Endoplasmic Reticulum
Diseases caused due to ER stress
o The Burnham Institute for Medical Research, La Jolla, California, USA
o Researchers: Chunyan Xu, Beatrice Bailly-Maitre and John C. Reed
o ER stress can cause hypoxia, neurodegenerization, heart disease, and diabetes
o BI-1 (Bax-inhibitor) is an ER protein that suppresses cell death pathways (apoptosis)
o The Bax-Inhibitor is secreted when ER undergoes stress in effort to compensate for damage and causes the unfolded protein response (UPR)
o Although the ER stress is enigmatic, here are some possible factors that could affect the ER:
• Deprivation of glucose
• Viral infection
Insertion of Secretory Proteins into the membrane
o New York University
o Researcher: David Domingo Sabatini Ph.D., Doc. En Med.
o Research Summary: The effecting elements on the insertion of the proteins secreted in the Endoplasmic Reticulum into the membrane.
o Currently: Their research uses an artificial environment that allows them to trace specific proteins, their sorting, and the protein’s transfer to the membrane.
MLA Works Cited
"Endoplasmic Reticulum." Wikipedia, The Free Encyclopedia. 9 Oct. 2008
<http://en.wikipedia.org/wiki/Endoplasmic_reticulum>.
Beatrice Bailey-Maitre, Ph.D. “Role of BI-1 Protein in Brest Cancer Apoptosis.” The Burnham Institute for Medical Research. 10 Oct. 2008.
<http://www.cbcrp.org/RESEARCH/PageGrant.asp?grant_id=3756>
Beatrice Bailey-Maitre, Ph.D. “BI-1 regulates an apoptosis pathway linked to endoplasmic reticulum stress.” The Burnham Institute for Medical Research. 10 Oct. 2008.
<http://lib.bioinfo.pl/pmid:15304216>
Xu Chunyan, Beatrice Bailey-Maitre, and Reed John C. “Endoplasmic reticulum stress: cell life and death decisions.” The Journal of Clinical Investigations. 10 Oct. 2008.
< http://www.jci.org/articles/view/26373>
Sabatini, David Domingo, Ph.D., Doc. en Med. "David Domingo Sabatini Ph.D., Doc.
en Med." NYU Langone Medical Center. 2008. 9 Oct. 2008
<http://www.med.nyu.edu/research/sabatd01.html>.
Campbell, Neil A. Biology. 8th ed. San Francisco: Pearson Education, Inc., 2008.
“Endoplasmic_Reticulum.jpg” 10 October 2008.
<http://www.microscopy.fsu.edu/cells/endoplasmicreticulum/images/endoplasmicreticulumfigure1.jpg>
“ribos2.jpg” 10 Oct. 2008.
<http://www.cytochemistry.net/Cell-biology/ribos2.jpg>
“home_page_image.jpg” 10 Oct. 2008.
< http://pathology.ucsf.edu/oakes/images/home_page_image.jpg>
Maggie Fuller
Rough ER
The "rough" portion of the endoplasmic reticulum (RER) is so named because of the attached ribosomes on the cytoplasmic side of the RER sacs which give the organelle a granular appearance. This section of the ER is located closer to the nucleus than the smooth ER and is "continuous with the nuclear envelope" (Campbell 58). The ER itself is continuous, meaning that the membrane is a single unit, connecting seamlessly with the nuclear envelope. In plant cells, this membrane also forms intracellular connections via the plasmodesmata (Davidson). The rough membranes of the endoplasmic reticulum were first seen by Keith R. Porter, Albert Claude, and Ernest F. Fullam in 1945 when they created the first ever electron micrograph of an intact cell ("History").
Modification of Proteins
The ribosomes on the surface of RER create the ingredients for proteins. When these ingredients enter the RER sacs, they are modified into functioning proteins by adjusting the tertiary and quaternary structures of the proteins (Campbell 59). The type of proteins synthesized depends on the type of cell that encompasses the RER. For example, in white blood cells, RER produces antibodies, and in pancreatic cells, it produces insulin (Mallery). "Chaperone proteins" check that all proteins are folded properly before they are transported from the RER (Papp). We know very little about these proteins and research is being conducted to study the effects of high and low levels of chaperone.
Making More Membrane
The proteins synthesized in the RER either move into the Smooth Endoplasmic Reticulum or are used as part of the RER membrane. If the proteins are membrane proteins, they are inserted into the membrane, which over time grows and enlarges the organelle. The more active in protein synthesis the RER is, the more membrane it produces (Spurger). This makes the identification of highly protein-synthesizing cells very easy because the large RER region marks its activity.
Smooth ER (SER)
The membrane and proteins made in the RER move into the SER to be "transferred to other parts of the cell," usually to the Golgi Apparatus or the cell membrane for export ("Journey into the Cell:"). The SER is connected to the RER farther away from the nucleus. It is tubular in shape and does not have ribosomes attached to it. The specific functions of the SER are highly dependent upon the type of cell in which it exists. Here are a few of its many functions.
SER in Liver Cells
In liver cells, SER metabolizes glycogen and detoxifies many drugs (Spurger). You can see in the picture above how large the SER is in the liver cell. This is because the more the SER processes, the larger it becomes. This can be potentially harmful because it raises tolerance to drugs, increasing the likelihood of larger doses consumed by drug abusers and increasing tolerance to other essential drugs like antibiotics (Campbell 58).
SER in Muscle Tissue
In many muscle cells SER serves as a store of Calcium. When nerve impulses reach the muscle cell, the SER releases its Calcium (Campbell 59). This action works with Calcium pumps to contract the cell and allow the muscle to move (Spurger).
Production of Steroids
In the adrenal cortex, the SER is responsible for synthesis of many essential steroid hormones. The SER passes unfinished molecules back and forth with the mitochondria to make minor changes in the molecule until it is completely finished (King). In gonadal tissue, the ER contains an enzyme aromatase, which converts testosterone and androstenedione to estradiol (King). This function is incredibly important because the sensitivity of humans to sex hormone level fluctuations.
Works Cited
1)Black, Virginia H., et al. “Cholesterol and Steroid Synthesizing Smooth Endoplasmic Reticulum of Adrenocortical Cells Contains High Levels of Proteins Associated with the Translocation Channel.” Endocrinology 146.10 (2005): 4234-4249. Abstract. Endocrinology. 2005. The Endocrine Society. 13 Oct. 2008 <http://endo.endojournals.org/cgi/content/abstract/146/10/4234>.
2)Campbell, Neil A., et al. Biology: concepts and connections. 5th ed. 7 vols. San Francisco: Pearson, 2006. 50-69.
3)Davidson, Michael W. “The Endoplasmic Reticulum.” Molecular Expressions Cell Biology. 13 Dec. 2004. The Florida State University Research Foundation. 12 Oct. 2008 <http://www.microscopy.fsu.edu/cells/endoplasmicreticulum/endoplasmicreticulum.html>.
4)“History.” Ernest F. Fullam Inc. Ernest F. Fullam Inc. 13 Oct. 2008 <http://www.fullam.com/History.htm>.
5)“Journey into the Cell: The Endoplasmic Reticulum.” Biology. 2008. The New York Times Company. 12 Oct. 2008 <http://biology.about.com/library/weekly/aa041300a.htm>.
6)King, Michael W. “Steroid Hormones.” The Medical Biochemistry. 15 May 2008. Indiana University School of Medicine. 13 Oct. 2008 <http://themedicalbiochemistrypage.org/steroid-hormones.html>.
7)Mallery, Charles H. “Major Eukaryotic Cell Organelles.” University of Miami Department of Biology. 9 Oct. 2008. University of Miami. 11 Oct. 2008 <http://porpax.bio.miami.edu/~cmallery/150/cells/organelle.htm>.
8)Papp, Eszter, et al. “Changes of Endoplasmic Reticulum Chaperone Complexes, Redox State, and Impaired Protein Disulfide Reductase Activity in Misfolding {Alpha}1-Antitrypsin Transgenic Mice.” The FASEB Journal (Oct. 2006). 13 Oct. 2008 <http://www.fasebj.org/cgi/content/abstract/20/7/1018>.
9)Rinehart, Claire. “Eukaryotic Organelles.” Introduction to Molecular and Cell Biology, Biol. 220. 2004. Western Kentucky University. 12 Oct. 2008 <http://bioweb.wku.edu/courses/Biol22000/11Organelles/Lecture.html>.
10)Spurger, Linda. “Cell Biology.” Cell Biology Graduate Program. 5 Dec. 2003. The University of Texas Medical Branch. 13 Oct. 2008 <http://cellbio.utmb.edu/cellbio/>.